Sanofi agreed to pay $1 billion upfront to expand its antibody collaboration with Regeneron, extending the longtime immunology alliance built around Dupixent. The expansion focuses on additional early-stage programs, aiming to replicate antibody-driven momentum as Dupixent faces patent-cliff pressure. The deal signals that major pharma is still willing to lean on antibody platforms and partnership structures rather than fully internalizing discovery pipelines. For Regeneron, it also provides longer-dated financial runway tied to expanded R&D execution. For investors and partners, the headline is straightforward: large immunology alliances remain capital-efficient vehicles for replenishing oncology and inflammatory drug portfolios—especially when combined with clear milestone structures.